1. Field of the Invention
The invention concerns a method, an apparatus and a processing plant for the sterilization and/or heat treatment of products in particle form, e.g. bone meal, fish meal and other feedstuffs, in a horizontally-lying, rotatable pressure vessel.
2. Description of the Prior Art
It is known to sterilize bone meal and similar products in batches by heating the meal during stirring in a pressure vessel. The known pressure vessels for this purpose can be horizontally-lying vessels with a through-going horizonal axle which comprises mechanical stirring elements in the form of vanes which are secured to the vessel's through-going axle. Such a sterilization plant is characterized by high power consumption and risk of great wear and corrosion, in that the moving parts, i.e. the axle with the vanes, are constantly in contact with the product which is to be stirred/mixed. The risk of these parts suffering defects is thus very high, and the stirring is not as efficient as desirable.
The known types of apparatus with through-going, rotatable axle often have problems with the bearings and associated stuffing-boxes, namely where the axle passes the vessel walls. Here it is possible for the product to gain ingress to the stuffing-box and cause wear, one of the results being that the stuffing-boxes become leaky. There also hereby arises the possibility of the product being contaminated, possibly by non-sterile product remains, so that a batch which can be expected to be sterile nevertheless proves to be contaminated.
The present invention provides a method and apparatus which is not encumbered with the disadvantages of the known technique, and whereby a continuous mixing and uniform sterilization of the product is achieved with an optimum utilization of the vessel's capacity, while at the same time the risk of any defects arising is very small.
This is achieved by a method, and also where the pressure vessel is arranged to rotate and is provided with a built-in, inner helical-vane arrangement along the inner wall/jacket of the pressure vessel, said pressure vessel being closed and evacuated of air and heated, said heating being effected by a supply of steam to the jacket of the pressure vessel, and optionally by a supply of steam under pressure to the inside of the vessel, said heating and pressure treatment taking place for a given period of time, in that the process parameters are a function of the product to be treated, and said pressure vessel being made to rotate, said rotation giving rise to a mixing/movement of the particle-formed product, and a movement of the product from the one end of the pressure vessel to the other as a result of the inner helical-vane arrangement, said process vessel then being relieved of pressure, after which the process vessel is emptied of heat-treated/sterilized product and the batch process starts from the beginning.
By carrying out a mixing as disclosed, a continuous and constant mixing of the product takes place, so that the product is in constant movement and is heated uniformly, partly by the surfaces of the pressure vessel which, of course, are heated via the steam supply, and also by the supply of steam which optionally takes place inside the pressure vessel. There is hereby achieved a uniform processing of the product.
The apparatus according to the invention can be configured wholly or partly of stainless steel, so that corrosion by the meal, which in certain cases can be aggressive, is avoided.
By using a method according to the invention, there is achieved a continuous and efficient sterilization in relation to the chosen process parameters.
By using a method according to the invention, an optimum mixing and an optimum and uniform sterilization of the product is achieved.
By using a method according to the invention, an optimum utilization of the thermal characteristics of the steam is achieved.
By using a method according to the invention, a desired automation of the process is achieved.
By using a method according to the invention, it is achieved that the sterilized product is not contaminated during its removal.
The invention also concerns an apparatus for the sterilization and/or heat treatment of products in particle form, e.g. feedstuffs such as bone meal and fish meal, comprising a substantially horizontal and rotatable pressure-tight vessel. The apparatus also comprises a mixing arrangement provided in the vessel, said arrangement comprising a helical vane lying along the vessel's inner wall, called the outer vane, and a second helical vane called the inner vane fastened to said outer vane and at a distance from the inner wall, which vanes extend from the one end of the vessel towards the other.
There is hereby achieved a continuous mixing and uniform sterilization of the product with an optimum utilization of the vessel's capacity, while at the same time the risk that defects may arise is very small.
By using an apparatus according to the invention the product is conveyed forwards and backwards over the heating surfaces, i.e. the jacket, and at the same time does not clump together with the risk of a subsequent heterogeneous mixing of the product.
By using an apparatus according to the invention the sterilized product is not contaminated during removal.
By configuring an apparatus according to the invention, an expedient construction of the apparatus is achieved, so that the possibility is provided of being able to use and control all functions during operation, i.e. without having to stop the rotation of the vessel.
By using an apparatus according to the invention, it is achieved that the risk of leakage is minimized.
The invention also concerns a processing plant for the production of sterile bone meal while using the method and the apparatus as disclosed, and where the processing apparatus forms the boundary between the non-sterile and the sterile areas of the plant. It is hereby achieved that a contamination of the sterilized product does not occur during the full handling of the product from the moment that it is brought into the hall for processing until it again leaves the hall after the processing has taken place.